diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableChecker.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableChecker.java
index 6623f705535..0de99730e2b 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableChecker.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableChecker.java
@@ -310,7 +310,7 @@ private Violation isFieldImmutable(
         // accumulating the path to the error from the top-level class being checked
         state.reportMatch(
             buildDescription(tree.get())
-                .setMessage("@Immutable classes cannot have non-final field")
+                .setMessage("@Immutable classes cannot have non-final fields")
                 .addFix(SuggestedFix.addModifier(tree.get(), Modifier.FINAL, state))
                 .build());
         return Violation.absent();
@@ -463,29 +463,15 @@ public Violation visitType(Type type, Void s) {
 
   // Anonymous classes
 
-  /** Check anonymous classes whose direct supertype is {@code @Immutable}. */
+  /** Check anonymous implementations of {@code @Immutable} types. */
   private Description handleAnonymousClass(ClassTree tree, VisitorState state) {
-    Violation info = checkAnonymous(tree, state);
-    if (!info.isPresent()) {
-      return Description.NO_MATCH;
-    }
-    String message = "Mutable because " + Joiner.on(", ").join(info.path());
-    return buildDescription(tree).setMessage(message).build();
-  }
-
-  private Violation checkAnonymous(ClassTree tree, VisitorState state) {
     ClassSymbol sym = ASTHelpers.getSymbol(tree);
     if (sym == null) {
-      return Violation.absent();
-    }
-    ImmutableSet<String> typarams = immutableTypeParametersInScope(sym);
-    Type superClass = sym.getSuperclass();
-    if (superClass == null) {
-      return Violation.absent();
+      return Description.NO_MATCH;
     }
-    ImmutableAnnotationInfo annotation = getImmutableAnnotation(superClass.tsym);
-    if (annotation == null) {
-      return Violation.absent();
+    Type superType = immutableSupertype(sym, state);
+    if (superType == null) {
+      return Description.NO_MATCH;
     }
     // We don't need to check that the superclass has an immutable instantiation.
     // The anonymous instance can only be referred to using a superclass type, so
@@ -497,7 +483,16 @@ private Violation checkAnonymous(ClassTree tree, VisitorState state) {
     // public static <@Immutable T> ImmutableBox<T> create(T t) {
     //   return new ImmutableBox<>(t);
     // }
-    return areFieldsImmutable(Optional.of(tree), typarams, ASTHelpers.getType(tree), state);
+    ImmutableSet<String> typarams = immutableTypeParametersInScope(sym);
+    Violation info =
+        areFieldsImmutable(Optional.of(tree), typarams, ASTHelpers.getType(tree), state);
+    if (!info.isPresent()) {
+      return Description.NO_MATCH;
+    }
+    String reason = Joiner.on(", ").join(info.path());
+    String message = String.format(
+        "Class extends @Immutable type %s, but is not immutable: %s", superType, reason);
+    return buildDescription(tree).setMessage(message).build();
   }
 
   // Strong behavioural subtyping
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java
index 4f16b286410..e0ba7e06868 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java
@@ -96,6 +96,7 @@ private static ImmutableMap<String, ImmutableAnnotationInfo> getBootstrapClasses
         .add("org.joda.time.Instant")
         .add("org.joda.time.LocalDate")
         .add("org.joda.time.LocalDateTime")
+        .add("org.joda.time.format.DateTimeFormatter")
         .add(com.google.common.primitives.UnsignedLong.class)
         .add(com.google.common.base.Converter.class)
         .add("com.google.protobuf.ByteString")
@@ -113,10 +114,13 @@ private static ImmutableMap<String, ImmutableAnnotationInfo> getBootstrapClasses
         .add(com.google.common.collect.ImmutableList.class, "E")
         .add(com.google.common.collect.ImmutableMultiset.class, "E")
         .add(com.google.common.collect.ImmutableMap.class, "K", "V")
+        .add(com.google.common.collect.ImmutableBiMap.class, "K", "V")
         .add(com.google.common.collect.ImmutableMultimap.class, "K", "V")
         .add(com.google.common.collect.ImmutableRangeMap.class, "K", "V")
         .add(com.google.common.collect.ImmutableTable.class, "R", "C", "V")
         .add(com.google.common.base.Optional.class, "T")
+        .add(com.google.common.base.Splitter.class)
+        .add(com.google.common.base.Joiner.class)
         .add(com.google.common.collect.Range.class, "C")
         .build();
   }
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableCheckerTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableCheckerTest.java
index 9470ab0cc07..daeb3bbd70f 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableCheckerTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ImmutableCheckerTest.java
@@ -755,6 +755,31 @@ public void positiveAnonymous() {
         .doTest();
   }
 
+  @Test
+  public void positiveAnonymousInterface() {
+    compilationHelper
+        .addSourceLines(
+            "threadsafety/Super.java",
+            "package threadsafety;",
+            "import com.google.errorprone.annotations.Immutable;",
+            "@Immutable interface Super {",
+            "}")
+        .addSourceLines(
+            "threadsafety/Test.java",
+            "package threadsafety;",
+            "import com.google.errorprone.annotations.Immutable;",
+            "class Test {{",
+            "  new Super() {",
+            "    // BUG: Diagnostic contains: non-final",
+            "    int x = 0;",
+            "    {",
+            "      x++;",
+            "    }",
+            "  };",
+            "}}")
+        .doTest();
+  }
+
   @Test
   public void negativeParametricAnonymous() {
     compilationHelper